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Unformatted text preview: H when H holds (i.e., whether the actual signiﬁcance level is close to the nominal signiﬁcance level). When the sample size (or counts) are small, the Fisher’s exact test can be used, which is better than the χ 2 test for small samples. Summary: Fisher’s Exact Test The Fisher’s exact test computes the exact p-value by performing probability calculations conditioning on the marginal totals being ﬁxed , i.e., if the marginal totals are ﬁxed, what is the probability of observing the data or more extreme when H holds . In general, the exact p-value of a Fisher’s exact test can be obtained using the hyper-geometric distribution. The Fisher’s exact test is only used for 2 × 2 tables. Fisher’s exact test The Fisher’s exact test is preferred when the sample size is small. When the sample size is large, the χ 2 test may still be more desirable....
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